Interrupting message migration in action creates message duplicates across separate Targets

1. Have 4 brokers.
2. Send 10k messages to Broker #4 (3rd ordinal).
3. Start message migration.
4. After some messages have been received on Broker#1 (0 ordinal), block the target address.
This would cause drain.sh to switch target to Broker#2 (1 ordinal).
5. Take a look at message counts on both Target brokers when drainer has finished.
Combined count would be >10k initially sent messages.